Is the parasitization rate of<Emphasis Type="Italic">Diaeretiella rapae</Emphasis> influenced when<Emphasis Type="Italic">Brevicoryne brassicae</Emphasis> feeds on<Emphasis Type="Italic">brassica</Emphasis> plants?

The development time and parasitization rate ofDiaeretiella rapae (M’Intosh) onBrevicoryne brassicae (L.) feeding on differentBrassica cultivars was studied in the laboratory at 20°C. The shortest development time from egg to adult parasitoid was 11.6 days on cabbage cv. ‘Yalova 1’ and the longest was 12.1 days on turnip cv. ‘Antep’ and rapeseed cv. local variety. Females lived significantly longer than males on the host plants used in the study. Females and males had the shortest longevity on rapeseed at 11.1 and 5.1 days, respectively. The highest percent parasitism ofB. brassicae byD. rapae was found on cabbage (40.20%), and the lowest was recorded on turnip (32.64%). Our results demonstrate that parasitism rate could be influenced by the plant quality, probably due to the nutritional status of the aphids or to toxic compounds ingested through the plant. Cabbage, cauliflower and broccoli were found to be suitable plants for the parasitoid, considering the development time of pre-adults, and the parasitization rate ofD. rapae onB. brassicae. http://www.phytoparasitica.org posting Jan. 23, 2007.     

Differing susceptibility to<Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> formulations of<Emphasis Type="Italic">Thaumetopoea wilkinsoni</Emphasis> populations between forests with different<Emphasis Type="Italic">Bt</Emphasis> management in Israel

The susceptibility ofThaumetopoea wilkinsoni larvae toBacillus thuringiensis (Bt) formulations was screened in 2003 and 2004. Eggs and larvae were collected from pine forests in 11 geographical locations in Israel. Larval mortality bioassays were conducted with commercial formulations (Delfin WG, Dipel DF and Foray 48B) at concentrations ranging from 0.001% to 0.1%. Significant differences in susceptibility toBt were recorded among populations that were treated withBt intensively, frequently, or never. The mortality recorded in a population that was never treated withBt was twice that in an intensivelyBt-treated population. The correlation between susceptibility toBt and the possible resistance to the microbe is discussed. http://www.phytoparasitica.org posting Jan. 31, 2007.     

Adsorption of OP<Subscript>1</Subscript>-related bacteriophages requires the gene encoding a TonB-dependent receptor-like protein in <Emphasis Type="Italic">Xanthomonas</Emphasis><Emphasis Type="Italic">oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis>

Xanthomonas oryzae pv. oryzae strain T7174R is lysed by bacteriophage OP_1h and OP_1h2. Three mutants tolerant to both OP_1h and OP_1h2 were isolated by transposon mutagenesis. The mutants had an insertion of the transposon in XOO1687, which is predicted to encode a TonB-dependent receptor gene. Plasmid pHMIroNB that contained XOO1687 of T7174R was constructed, and the mutant was transformed with the plasmid. The transformant recovered sensitivity to OP_1h and OP_1h2. Electron microscopic analysis demonstrated that OP_1h and OP_1h2 can adsorb to the wild type and the transformant, but they could not adsorb to the phage-tolerant mutant. These results suggest that the TonB-dependent receptor gene relates to adsorption and infection of T7174R by OP_1h2 and OP_1h. Y. Inoue and S. Tsuge have contributed equally to this work.     

Competition between Solanum nigrum and pepper in the presence of Meloidogyne incognita

The influence of the root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood on the competitive relationships between pepper (Capsicum annuum L.) and Solanum nigrum L. (black nightshade) was investigated in a glasshouse experiment. Seven competition treatments were set up: two intraspecific for the crop and the weed and five interspecific treatments in which the emergence of S. nigrum plants was progressively delayed with respect to that of the pepper. Nematodes reproduced in every inoculated plant and their multiplication rates were high in both pepper and S. nigrum. The parasite reduced all growth and yield parameters of the crop, but did less harm to the weed. The negative effect of S. nigrum on pepper peaked in the treatment in which the weed and pepper plants emerged together. S. nigrum was a stronger competitor than pepper under both nematode-infested and nematode-free conditions. The effect of nematodes on pepper yield was less than that of competition, but both appeared to be additive.     

Mechanisms of resistance in<Emphasis Type="Italic">Lycopersicon</Emphasis> germplasm to the whitefly<Emphasis Type="Italic">Bemisia argentifolii</Emphasis>

The silverleaf whiteflyBemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) [also known as strain B of the sweetpotato whiteflyB. tabaci (Gennadius)] is a major pest of tomatoes due to both feeding damage and transmission of plant viruses. Certain wild species ofLycopersicon have demonstrated high levels of resistance to the pest. Greenhouse studies were undertaken to quantify the effects on whitefly behavior and mortality of individual, resistant plants selected from three accessions ofL. pennellii (Corr.) D’Arcy (LA 1340, LA 1674 and LA 2560), five accessions ofL. hirsutum f.typicum Humb. & Bonpl. (LA 386, LA 1353, LA 1777, PI 127826 and PI 127827) and one accession ofL. hirsutum f.glabratum C.H. Mull. (PI 126449). In no-choice experiments, fewer adults settled on leaflets of the wild species and deposited 75–100% fewer eggs compared to the cultivated tomato,L. esculentum Mill. Adult mortality ranged from 77–100% on wild accessions but was only 1% onL. esculentum. Most dead adults were trapped in glandular trichome exudates. The effects of these resistant accessions onB. argentifolii were mechanically transferable by appressing the trichome exudates onto the leaves of the susceptible tomato, indicating an association between the factors mediating the resistance and the glandular trichomes. Laboratory studies evaluated the repellent, fumigant and residual toxic effects of representative constituents of trichome exudates onB. argentifolii adults by using selected concentrations and probit analyses. RC₅₀ values (estimated concentration to repel 50% of the adults) and LC₅₀ values for fumigant and residual toxicity indicated that 2-tridecanone had low levels of repellent and residual toxicity activity; that 2-undecanone had high levels of repellent and fumigant activity; and that ginger oil (composed, in part, of sesquiterpene hydrocarbons) had high levels of repellent and residual toxicity activity. These studies suggest that multi-factor resistance exists in wild tomato germplasm. By combining genetically the observed chemical constituents of resistance into a single germplasm, the resulting resistance may be more difficult forB. argentifolii to overcome. http://www.phytoparasitica.org     

Sélectivité du carbétamide

La pénétration, le transfert et la métabolisation du carbétamide ont étéétudiés dans une plante sensible (l'orge), une plante moyennement sensible (la luzerne) et une plante résistante (la laitue). Le Carbétamide est un peu plus facilement transporté vers les feuilles dans l'orge et sa métabolisation est plus rapide dans la luzerne. Ces différences pourraient être à l'origine de la différence de sensibilité entre orge et luzerne, mais aucun des résultats obtenus explique la différence de sensibilité entre orge et laitue.     

Characteristics of a <Emphasis Type="Italic">Plasmopara angustiterminalis</Emphasis> isolate from <Emphasis Type="Italic">Xanthium strumarium</Emphasis>

Leaves of Xanthium strumarium infected with downy mildew were collected in the vicinity of a sunflower field in southern Hungary in 2003. Based on phenotypic characteristics of sporangiophores, sporangia and oospores as well as host preference the pathogen was classified as Plasmopara angustiterminalis. Additional phenotypic characters were investigated such as the size of sporangia, the number of zoospores per sporangium and the time-course of their release. Infection studies revealed infectivity of the P. angustiterminalis isolate to both X. strumarium and Helianthus annuus. Inoculation of the sunflower inbred line, HA-335 with resistance to all known P. halstedii pathotypes, resulted in profuse sporulation on cotyledons and formation of oospores in the bases of hypocotyls. Infections of sunflower differential lines often led to damping-off. Molecular genetic analysis using simple sequence repeat primers and nuclear rDNA sequences revealed clear differences to Plasmopara halstedii, the downy mildew pathogen of sunflower.     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.     

Isolation of pathogenicity- and gregatin-deficient mutants of <Emphasis Type="Italic">Phialophora gregata</Emphasis> f. sp. <Emphasis Type="Italic">adzukicola</Emphasis> through <Emphasis Type="Italic">Agrobacterium tumefaciens</Emphasis>-mediated transformation

Phialophora gregata f. sp. adzukicola, a causal agent of brown stem rot in adzuki beans, produces phytotoxic compounds: gregatins A, B, C, D, and E. Gregatins A, C, and D cause wilting and vascular browning in adzuki beans, which resemble the disease symptoms. Thus, gregatins are considered to be involved in pathogenicity. However, molecular analyses have not been conducted, and little is known about other pathogenic factors. We sought to isolate nonpathogenic and gregatin-deficient mutants through Agrobacterium tumefaciens-mediated transformation (ATMT) for cloning of pathogenicity-related genes. The co-cultivation of P. gregata and A. tumefaciens for 48 h at 20°C with 200 μM acetosyringone resulted in approximately 80 transformants per 10⁶ conidia. The presence of acetosyringone in the A. tumefaciens pre-cultivation period led to an increase in T-DNA copy number per genome. Of 420 and 110 transformants tested for their pathogenicity and productivity of gregatins, one nonpathogenic and three gregatin-deficient mutants were obtained, respectively. The nonpathogenic mutant produced gregatins, whereas the gregatin-deficient mutants had pathogenicity comparable to the wild-type strain. This is the first report of ATMT of P. gregata. Further analysis of these mutants will help reveal the nature of the pathogenicity of this fungus including the role of gregatin in pathogenesis.     

Environmental persistence of<Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> products tested under natural conditions against<Emphasis Type="Italic">Thaumetopoea wilkinsoni</Emphasis>

Information on persistence ofBacillus thuringiensis (Bt) is needed to improve the microbial pest management programs against the pine processionary mothThaumetopoea wilkinsoni in pine forests in Israel. The persistence of the microbe under natural conditions of rain and sunlight was evaluated and is documented here for the first time. Pine saplings were sprayed with three commercialBt products, Foray 48B, Delfin WG and Dipel DF, all used at 32,000 IU mg⁻¹ in a formulation with 1% (w/v) of condensed milk. In experiments conducted in November and December of 2004, the saplings were either exposed to rain and sunlight or were sheltered to avoid these environmental factors. The lowest rainfall recorded in the 8-day experiments was 16.5 mm (test 2) and the heaviest was 71.1 mm (test 1). Solar irradiation ranged from 9.4 to 10.9 MJ m⁻². The minimum temperature was close to 10°C and the maximum was less than 23°C. Needles of the treated saplings and their controls were sampled after 0, 1, 5 and 8 days, and were fed to 1 ^st or 2 ^nd instar larvae. Dipel DF persisted better than Delfin WG and still retained its initial activity of 80–100% mortality on day 8 at low rainfall (test 2). Dripping ofBt from upper to lower branches was quantified with the larval bioassays. The milk formulation proved to be an effective rain-fasting adjuvant. http://www.phytoparasitica.org posting May 4, 2007.     

Differential interactions of <Emphasis Type="Italic">Verticillium longisporum</Emphasis> and <Emphasis Type="Italic">V. dahliae</Emphasis> with <Emphasis Type="Italic">Brassica napus</Emphasis> detected with molecular and histological techniques

The differential interactions of V. longisporum (VL) and V. dahliae (VD) on the root surface and in the root and shoot vascular system of Brassica napus were studied by confocal laser scanning microscopy (CLSM), using GFP tagging and conventional fluorescence dyes, acid fuchsin and acridin orange. VL and VD transformants expressing sGFP were generated by Agrobacterium-mediated transformation. GFP signals were less homogenous and GFP tagging performed less satisfactory than the conventional fluorescence staining when both were studied with CLSM. Interactions of both pathogens were largely restricted to the root hair zone. At 24 h post-inoculation (hpi), hyphae of VL and VD were found intensely interwoven with the root hairs. Hyphae of VL followed the root hairs towards the root surface. At 36 hpi, VL hyphae started to cover the roots with a hyphal net strictly following the grooves of the junctions of the epidermal cells. VL started to penetrate the root epidermal cells without any conspicuous infection structures. Subsequently, hyphae grew intracellularly and intercellularly through the root cortex towards the central cylinder, without inducing any visible plant responses. Colonisation of the xylem vessels in the shoot with VL was restricted to individual vessels entirely filled with mycelium and conidia, while adjacent vessels remained completely unaffected. This may explain why no wilt symptoms occur in B. napus infected with VL. Elevated amounts of fungal DNA were detectable in the hypocotyls 14 days post-inoculation (dpi) and in the leaves 35 dpi. Root penetration was also observed for VD, however, with no directed root surface growth and mainly an intercellular invasion of the root tissue. In contrast to VL, VD started ample formation of conidia on the roots, and was unable to spread systemically into the shoots. VD did not form microsclerotia in the root tissue as widely observed for VL. This study confirms that VD is non-pathogenic on B. napus and demonstrates that non-host resistance against this fungus materializes in restriction of systemic spread rather than inhibition of penetration.     

Effect of seed treatment of<Emphasis Type="Italic">Arachis hypogaea</Emphasis> with<Emphasis Type="Italic">Bacillus subtilis</Emphasis> on nodulation in biocontrol of southern blight (<Emphasis Type="Italic">Sclerotium rolfsii</Emphasis>) disease

The employment of formulatedBacillus subtilis for peanut seeds (Arachis hypogaea cv. ‘Shulamit’) counteracted the destructive effects of the seedborne pathogenSclerotium (Athelia)rolfsii on the nodulation, leghemoglobin and nitrogenase activity of peanuts. Moreover, the changes in crop vigor index, total nitrogen content and survivability of bothRhizobium spp. andB. subtilis have been related to compatibility and even an occasional synergism between them. http://www.phytoparasitica.org posting Nov. 12, 2006.     

Evaluation of the durability of the <Emphasis Type="Italic">Barley yellow dwarf virus</Emphasis>-resistant <Emphasis Type="Italic">Zhong ZH</Emphasis> and <Emphasis Type="Italic">TC14</Emphasis> wheat lines

Serial passage experiments (SPE) of a Barley yellow dwarf virus-PAV (BYDV-PAV) isolate were performed on Zhong ZH and TC14 wheat lines to evaluate the durability of their resistance to BYDV. At different passage numbers (from the 2nd to the 114th), biological properties of the produced isolates were recorded either by monitoring infection percentages and virus titers of the first 3 weeks of viral infection or by measuring their impact on yield components. Statistical analyses using the area under pathogen progress curves and the area under concentration progress curves demonstrated that these two resistant lines induce, after only a few passages, a selection of variant(s) with significantly modified infection abilities. Isolates resulting from SPE performed on these lines induced important decreases of yield components. These results indicate that the use of Zhong ZH and TC14 lines in BYDV-resistant breeding programmes should be approached with caution.     

Susceptibility and resistance of <Emphasis Type="Italic">Beta vulgaris</Emphasis> subsp. <Emphasis Type="Italic">maritima</Emphasis> to foliar rub-inoculation with <Emphasis Type="Italic">Beet necrotic yellow vein virus</Emphasis>

Four lines (designated MR0, MR1, MR2, and M8) from 13 accessions of Beta vulgaris subsp. maritima were selected on the basis of phenotypes produced after foliar rub-inoculation with Beet necrotic yellow vein virus (BNYVV). The susceptible phenotype developed bright yellow local lesions, whereas the resistant phenotype had symptoms ranging from no visible lesions to necrotic lesions at the inoculation site. MR1 and MR2 lines had a resistant phenotype depending on the isolate and the MR0 line was susceptible to all isolates of BNYVV tested. The M8 line was highly susceptible; the virus spread systemically and caused severe stunting. These plant lines will be useful for distinguishing BNYVV isolates having different pathogenicities, especially those controlled by RNA3 and/or RNA5.     

<Emphasis Type="Italic">In vitro</Emphasis> screening for sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis>L.) resistant calli to <Emphasis Type="Italic">Diaporthe helianthi</Emphasis> fungal culture filtrate

Diaporthe helianthi the causal agent of sunflower (Helianthus annuus) stem canker, causes significant reductions in yield and oil content in most sunflower-growing areas. With the aim of enhancing host resistance, we selected in vitro sunflower calli against culture filtrates of two pathogen isolates (7/96 and 101/96). This technique may be an effective and rapid tool to discriminate the most virulent D. helianthi isolate and to screen for host resistance in the early stage of a breeding programme. Further investigation on the mechanisms involved in defence pathways showed no induction of salicylic acid and pathogenesis-related proteins in calli, indicating that the host resistance is not associated with Systemic Acquired Resistance but probably other biochemical mechanisms.     

<Emphasis Type="Italic">Bchex</Emphasis> virulence gene of <Emphasis Type="Italic">Botrytis cinerea</Emphasis>: characterization and functional analysis

We previously identified Bchex as a highly expressed gene during filamentous growth in Botrytis cinerea. The gene encodes the principal protein of the Woronin body and has been shown to seal septal pores in response to cellular damage. In the present study, Southern blot analysis of genomic DNA indicated that the gene exists as a single copy in the B. cinerea genome. The gene was differentially expressed during various developmental stages: expression was high in germinating conidia and the mycelial stage and lower in resting conidia and the appressorial stage. For functional analyses, homologous recombination was used to obtain a ΔBchex knockout mutant. Growth of the mutant was strongly reduced growth in complete medium and in defined media with sucrose, fructose or pectin as the carbon source. After detached tomato leaves were inoculated with the Bchex mutant, lesion development was markedly reduced compared to the control, suggesting that Bchex participates in normal growth, germination and virulence of this fungus.     

Occurrence of<Emphasis Type="Italic">Rhyacionia frustrana</Emphasis> on<Emphasis Type="Italic">Pinus brutia</Emphasis> in the Aegean Region of Turkey

The Nantucket pine tip moth (Rhyacionia frustrana (Comstock) (Lep., Tortricidae)) has been found on Turkish red pine (Pinus brutia L.) in the Aegean Region of Turkey. http://www.phytoparasitica.org posting Nov. 12, 2006     

Biofilm formation and resistance to bactericides of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">theae</Emphasis>

Biofilm-grown cells of Pseudomonas syringae pv. theae (P.s.theae) wild-type strain K9301 on abiotic surface had remarkable resistance to kasugamycin in comparison to planktonically grown cells; however, the biofilm-grown cells of K9301 had the same sensitivity to copper sulfate. Because both the lesser biofilm-forming strain K9301S3 and enhanced biofilm-forming strain K9301-6 also had remarkable biofilm resistance to kasugamycin just as K9301 did and because epigallocatechin gallate, which enhanced biofilm formation of P.s.theae, had no effect on biofilm resistance to kasugamaycin, the degree of biofilm formation was not correlated with the antibiotic susceptibilities. In addition, K9301 and K9301S3 had less sensitivity to kasugamycin but had high sensitivity to copper sulfate on nonwounded leaf surfaces. These results indicate a possibility that the mechanism of P.s.theae biofilm resistance to bactericide functions on both abiotic and nonwounded leaf surfaces.     

Note: Does<Emphasis Type="Italic">Liriomyza cicerina</Emphasis> affect the yield of chickpeas (<Emphasis Type="Italic">Cicer arietinum</Emphasis>)?

Liriomyza cicerina (Rondani, 1875) (Diptera: Agromyzidae) is an important pest on chickpea (Cicer arietinum L.) in some regions of Turkey. The objective of this study was to determine whether the populations ofL. cicerina on different varieties of chickpea plants during the 2004 and 2005 production seasons affected yield in Sanliurfa province. The trials were carried out using eight different varieties of chickpea with three replicates. During each season, larval densities on leaves were assessed weekly. TheL. cicerina larval population was lowest on four varieties for both seasons. There were very minor differences in yield among the eight varieties in the production seasons. There was no correlation found between larval density and yield loss. http://www.phytoparasitica.org posting Jan. 14, 2007.     

Molecular characterization and PCR detection of the melon pathogen <Emphasis Type="Italic">Acremonium</Emphasis><Emphasis Type="Italic">cucurbitacearum</Emphasis>

Acremonium cucurbitacearum is a soil-borne pathogen that causes collapse of muskmelon and watermelon plants. Cluster analysis based on RAPD patterns, obtained from use of 25 primers, divided isolates of A. cucurbitacearum from Spain and USA into two major groups. Most isolates from the USA fell into group 1, however, genetic similarity was not highly correlated with geographical origins or with previously established VCG groups. Analysis of 5.8S-ITS sequences showed very little sequence variation among isolates of A. cucurbitacearum, most had identical 5.8S-ITS sequence. Nodulisporium melonis, previously reported to cause a similar disease in Japan, had a 5.8S-ITS sequence that was identical to that of isolate A-419 proposed as the type strain of A cremonium cucurbitacearum suggesting that the two fungal pathogens should be considered a single species. Phylogenetic analysis, based on the 5.8S-ITS region, indicated that A cremonium cucurbitacearum is a monophyletic taxon more closely related to Plectosphaerella cucumerina than to other species of the genus Acremonium. Based on the 5.8S-ITS nucleotide sequence, a polymerase chain reaction was designed and used for specific detection of A. cucurbitacearum in diseased plants.